1. Field of the Invention
This invention relates to rotary stepping actuators that convert linear reciprocating motion to stepwise rotary motion, clockwise and backward, through a predetermined angle.
2. Discussion of the Background
Many industrial machines are required to produce stepwise rotary motion, forward and backward, through a given angle. To fulfill this requirement, the inventor proposed a stepping actuator that converts the reciprocating motion of each of a pair of pistons to stepwise forward or backward rotary motion through a given angle in Japanese Patent Application No. 354183 of 1992.
This stepping actuator comprises an outer frame that constitutes a hydraulic cylinder containing a pair of axially moving members serving as pistons. Through the axially moving members are passed a common rotating power output member. Either one of the outer frame and axially moving members has peripheral grooves that are alternately tilted in opposite directions with respect to the generator and connected to each other at both ends thereof to make up an endless circulating chain of grooves, while the other has projections to fit in the grooves described above.
A mechanism is provided for each circulating chain of grooves to allow the projections to select one adjoining groove after another when the axially moving member changes the direction of motion at each end thereof. The groove selection mechanism are designed to cause the projections to select the adjoining grooves tilted in opposite directions, thereby causing one of the axially moving members to rotate forward and the other backward. The ends of both circulating grooves are connected by circumferentially extending grooves. An example of the groove selection mechanism comprises a "go" groove along which the projector moves toward one end thereof when the axially moving member makes a reciprocating motion and a "return" groove connected thereto, with a step provided between the two grooves that makes the "return" groove deeper than the "go" groove.
Though simple in construction and capable of making a desired stepped rotation, forward or backward, this mechanism does not have adequate torque to hold the output shaft in position after it has been rotated stepwise by the motion of the axially moving member. Therefore, the output shaft continues to rotate when an overload is applied thereon. When some excessive load or disturbance acts during the motion of the axially moving member, in addition, each projection of the groove selection mechanism reciprocates in the same groove instead of moving to the desired adjoining groove. Then, the output shaft moves back and forth within a limited angular path without making a unidirectional rotation. It has therefore been desired to realize a mechanism to ensure that the output shaft makes a stable unidirectional rotation.